The students were reportedly giving presentations on Native American culture to some of the younger students at the private Quaker school when they and and their teacher, Amy Conrey Andreas, were suddenly ushered into a conference room.

The high school students were in Washington DC for a week and delivering a presentation on Native American culture when they were whisked away.

Then, before the students could figure out what was going on, Mrs Obama walked in.

The former First Lady reportedly had an appointment with one of her daughter Sasha's counsellors. But as she was just about to leave, the counsellors requested her to say a quick hello to the students, which she agreed.

Mrs Obama, however, did not just say a quick hello to the students. She decided to spend her day with the young men and women of the Blackfeet Nation.

Michelle Obama surprised a group of students from Blackfeet Nation (above) who were visiting Sidwell Friends as part of a cultural exchange programme.

For the next few hours, the nine students and their very emotional teacher hugged, posed for selfies and listened as Mrs Obama gave them an inspirational speech on success, privilege and the importance of education.

"It is going to be so important for you to be strong leaders so you can help your communities. That was my whole thing when I thought about law school, when I thought about what I wanted to do," the former First Lady told the students.

She added that she didn't keep practising law because she wanted to pick a career that allowed her to go back to her neighbourhood and her community.

"But I had to get the education and the experience to bring something back and just think about it now. We're about to build a multi-million dollar library right in my neighbourhood.The presidential library is going to be located 10 minutes from where I grew up," the First Lady said.